1. Field of the Invention
This invention relates to a drying apparatus for drying semiconductor substrates and a method for drying semiconductor substrates, especially suitable for application to a semiconductor substrate dryer configured to dry semiconductor substrates by blowing an evaporated organic solvent like isopropyl alcohol (IPA) onto the semiconductor substrates.
2. Description of the Related Art
An apparatus currently used in a rinse process of semiconductor wafers is configured, as shown in FIG. 1, to introduce a semiconductor waver 105 into rinse chambers 101, 102, 103 and a dry chamber 104 filled with IPA vapor to rinse and dry the semiconductor wafer 105. There are various methods as this rinsing process of the semiconductor wafer 105. First one (processing method 1) of them first introduce the semiconductor wafer 105 into the rinse tank 103 and then introduce it into the dry chamber 104 to dry it. The second rinsing method (processing method 2) first introduce the semiconductor wafer 105 into the rinse chambers 102 and 103, sequentially, and thereafter introduce it into the dry chambers 104 to dry it. The third rinsing method (processing method 3) first introduce the semiconductor wafer into the rinse chambers 101, 102 and 103, sequentially, and thereafter introduce it into the dry chamber 104 to dry it. In these processing method 1, processing method 2 and precessing method 3, the semiconductor wafer 104 always passes the dry chamber 104 for drying processing. Therefore, processing performance in the rinsing process of the semiconductor wafer 105 is determined by the drying processing time. Additionally, progressively enlarged sizes of semiconductor wafers have invited an increase of heat capacity of wafers to be dried, and the rinsing process of semiconductor wafers is rate-determined by the drying processing.
Among drying apparatuses actually used in the drying processing of semiconductor wafers, the major one is a drying apparatus employing a so-called IPA direct displacement drying system which is configured to dry these wafers by displacing water regaining on semiconductor wafer surfaces with IPA vapor of a high vapor pressure because of its good water replacing efficiency and drying performance. From the viewpoint of removing various problems such as generation of water marks, the drying apparatus employing the IPA direct displacement drying system is effective as compared with a spin dryer configured to repel water adhering on semiconductor wafer surfaces by a centrifugal force.
The conventional IPA vapor drying system is explained below. As shown in FIGS. 2A through 2D, the drier employing the IPS vapor drying system includes a dry chamber 111 filled with heated IPA vapor. To dry an object by using the drier, a semiconductor wafer 112 is first introduced at a high speed into the dry chamber 111 as shown in FIG. 2A, and then exposed to IPA vapor as shown in FIG. 2B. As a result, the semiconductor wafer 112 is heated to the temperature of the IPA vapor, and the IPA vapor displaces water on the surface of the semiconductor wafer 112 to thereby dry the semiconductor wafer 112. After that, as shown in FIGS. 2C and 2D, the semiconductor wafer 112 is slowly pulled up from the dry chamber 111 to complete the drying process. The IPA vapor drying system advantageously makes fewer water marks on dried semiconductor wafers and in electrically neutralizing semiconductor wafers.
However, the semiconductor wafer drying process using the above-explained IPA vapor drying apparatus involves the drawback that, due to a long dry-processing time, the through-put of the drying process is rate-determined by the drying process and results in decreasing the production capacity. In this connection, research has been made toward increasing the heating temperature of semiconductor wafers to reduce the dry-processing time. However, this approach invites problems such as bumping of IPA and producing an uneven drying effect.
Moreover, taking problems on the natural environment and residual organic substances into consideration, the industry has recently moved toward reducing the amount of organic materials to be used. Therefore, a drying method using the Marangoni effect and a controlled IPA vapor drying method has been mainly employed in drying apparatuses using IPA. These two drying methods are explained below.
A drying apparatus employing the drying method using the Marangoni effect is made up of a dry portion 121 and a rinse tank 123 filled with ultrapure water (DI water) 122 as shown in FIGS. 3A through 3D.
In a semiconductor wafer dry process using this drying apparatus, a semiconductor wafer 124 is first rinsed in the rinse tank 123 as shown in FIG. 3A. Then, the dry portion 121 contains a nitrogen (N.sub.2) gas atmosphere or ambient atmosphere. Next, as shown in FIG. 3B, mixed gas of N.sub.2 and IPA vapor is introduced into the dry portion 121 and blown onto the water surface of the ultrapure water 122 before the semiconductor wafer 124 is pulled out of the rinse tanks 123. As a result, as shown in FIG. 4, an IPA layer 125 is formed on the water surface. After that, as shown in FIG. 3C, the semiconductor wafer 124 is pulled out. When the semiconductor wafer 124 is pulled out, a gradient called meniscus portion is made along the interface between the surface of the semiconductor wafer 124 and the ultrapure water 122 as shown in FIG. 4, and the meniscus further increases by the IPA layer 125. While the semiconductor wafer 124 is pulled out, water remaining on its surface flows down along the meniscus portion. Then, the semiconductor wafer 124 is pulled out with no water remaining on its surface, and it is dried. Thereafter, as shown in FIG. 3D, N.sub.2 gas atmosphere is restored in the dry portion 121. In this manner, the dry process of the semiconductor wafer 124 is performed.
The drying apparatus employing the controlled IPA vapor drying method is made up of a dry tank 131 and a rinse tank 133 filled with ultrapure water 132 as shown in FIGS. 5A through 5D. In this drying apparatus, the dry tank 131 contains a N.sub.2 gas atmosphere as shown in FIG. 5A. In this status, after a semiconductor wafer 134 is rinsed in the rinse tanks 133, it is pulled out as shown in FIG. 5B, and transported into the dry chamber 131. Next, as shown in FIG. 5C, the dry tank 131 and the rinse tank 133 are blocked from each other by a cover (not shown), and mixed gas of N.sub.2 and IPA vapor is blown onto the semiconductor wafer from a nozzle (not shown) located in an upper position in the dry chamber 131. Thus, by displacing water remaining on the surface of the semiconductor wafer 134 by the IPA vapor, the semiconductor wafer 134 is dried. After that, as shown in FIG. 5D, the N.sub.2 gas atmosphere is restored in the dry tanks 131. In this manner, dry processing of the semiconductor wafer 134 is performed.
The controlled IPA vapor dry method of these two drying methods is certainly the method in place of the conventional IPA vapor dry method. However, as to conditions for drying semiconductor wafers, researches have been under trials and errors toward optimization of drying conditions.